This invention relates generally to a method for controlling a process and more particularly to a method for controlling a process, such as a chemical mechanical planarizaion process, in a multi-zonal processing apparatus.
Many types of processing apparatus include a plurality of zones within each of which some processing variable can be controlled in order to achieve some desired process result when a work piece is processed in the apparatus. For example, the processing apparatus may permit a variable or parameter such as pressure, temperature, voltage, current, or the like to be separately set in each of the plurality of zones to achieve a predetermined parameter distribution profile across the work piece. The predetermined profile, in turn, is intended to achieve a repeatable and predetermined result across the surface of the processed work piece. The process being controlled may be, for example, a polishing process, a planarization process such as a chemical mechanical planarization (CMP) process, a deposition process, or any other process practiced in an apparatus having a plurality of zones in which a process parameter can be adjusted in the various zones of the apparatus.
The multi-zonal processing apparatus and the process to be practiced in that apparatus, however, may suffer from the fact that there are a limited number of discrete zones within which the process parameter can be controlled. The limited number of discrete zones may cause the resulting parameter distribution profile to be discontinuous and segmented instead of the desired predetermined profile. In addition, discontinuities at the boundaries between zones may cause the profile to deviate even more from the ideal predetermined profile. Cross effects between adjacent zones and nonuniformities within zones may also complicate the resulting profile and hence the resulting process. Existing multi-zonal processing apparatus require extensive and multiple experimentation with intuitive dialing to properly set the parameters in each of the plurality of zones to achieve a desired result. Changes in the preprocessing condition of work pieces may require additional experimentation to adjust the parameters to the changed work pieces. Such required experimentation to properly set the apparatus is inconsistent with the efficient, reliable, and repeatable processing of work pieces.
Accordingly, a need exists for a method to automatically determine the optimum setting of parameters in the zones of a multi-zonal processing apparatus to repeatably and reliably achieve a parameter distribution profile that is a close approximation to a predetermined target parameter distribution profile.